There are several general types of polymer used to manufacture most high-performance caulks: silicones, polyurethanes, latex-acrylics, and solvent-based “block copolymer” synthetic rubbers (which include butyl as well as some of the newer proprietary synthetic formulations).

The best type of caulk for the job depends largely on the materials to which the caulk must bond. For bonding dissimilar materials (for example, wood to masonry, look for sealant that can handle a lot of joint movement.

For the most part, polyurethane caulks provide the best all-around performance for exterior applications, but they are more expensive than most other caulks and can be difficult to clean up (below).

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The table is meant only as a rough guide to help you narrow choices. (For instance, life expectancy and joint movement vary with the particular product.) While some caulks and sealants fit neatly into these broad categories, others, such as paintable silicone, are variations. There are also hybrid and specialty caulks with proprietary formulas that combine the properties of two or more types. As always, consult the manufacturer's specs on any particular product you are considering.
The table is meant only as a rough guide to help you narrow choices. (For instance, life expectancy and joint movement vary with the particular product.) While some caulks and sealants fit neatly into these broad categories, others, such as paintable silicone, are variations. There are also hybrid and specialty caulks with proprietary formulas that combine the properties of two or more types. As always, consult the manufacturer's specs on any particular product you are considering.

For more information, see the JLC Field Guide.